Absorption or diffusion for rear side walls?

[Diegel]

Hey guys. My room Is about 17.5' x 22' x 8'. My speakers are facing the short way. I know you usually want the speakers pointing the longer way but this is how I had to do it in my room because of a beam supporting the ceiling. I got plenty of bass trapping and first reflection points covered. I plan on putting a few diffusors on the rear wall behind the listening position. I was wondering wether I should put absorption or diffusion for the rear 1/3 of the side (17') walls. Thanks!

[Glenn Kuras]

You can use either. I will say for your back wall I would use both, absorption and diffusion.